This invention relates to a radiation sensitive resin composition. More particularly, it relates to a radiation sensitive resin composition which can be used as a resist particularly suitable for fine processing using a radiation such as ultraviolet ray, deep ultraviolet ray, X ray or charged particle beam.
In the field of fine processing, a representative of which is the production of an integrated circuit device, a lithographic technique is now being developed which enables fine processing in the order of subhalfmicron to be effected with good reproducibility. Representative resists which have recently been used in the lithographic process include positive resists using an alkali-soluble resin such as a novolak resin or the like and a quinonediazide type radiation sensitive compound. However, the performance of these resists approaches its limit and the use thereof in the fine processing in the order of subhalfmicron is accompanied by a great difficulty.
That is to say, these negative and positive resists have heretofore had such a problem that a sufficient theoretical focal depth cannot be achieved when a fine pattern of 0.35 .gamma.m or less is intended to be formed by a lithographic technique using an ultraviolet ray such as g ray (wavelength: 436 nm) or i ray (wavelength: 365 nm) or the like from a mercury vapor lamp.
Under such circumstances, research has been energetically conducted on a lithographic process using deep ultraviolet rays, X rays or electron beams which can achieve a broader depth of focus in the formation of a fine pattern. However, conventional resists have various problems in respects of pattern shape, sensitivity, contrast, development and the like when deep ultraviolet rays, X rays or electron beams are used. That is to say, in the case of deep ultraviolet rays, the light absorption of the resist is too great, and hence, in the case of a negative resist, the pattern shape tends to become a so-called reverse taper shape in which the lower part of the pattern is narrower than the upper part, while even in the case of a positive resist, the pattern shape becomes a taper shape and the sensitivity and contrast and the like are also lowered. In the case of a higher energy radiation such as X ray and electron beam, in general, the lowering of sensitivity is greater than in the case of deep ultraviolet ray, and particularly, in the case of a positive resist, such a phenomenon that the solubility in a developing solution is lowered upon irradiation with a radiation in some cases through the solubility should be originally increased upon irradiation.
On the other hand, as a next generation resist, attention is paid to a chemically amplified resist containing a radiation sensitive acid generator (namely, a compound generating an acid upon irradiation with a radiation), and this resist has such an advantage that the catalytic action of the acid generated increases the sensitivity to various radiations.
As those chemically amplified resists which show relatively good resist performance, there are known, for example, those containing a resin having a tert-butyl ester group or a tert-butoxycarbonyl group (for example, Japanese Patent Application Kokoku No. 2-27,660), those containing a resin having a silyl group (for example, Japanese Patent Application Kokai No. 3-44,290), those containing a resin having an acrylic acid component (for example, Japanese Patent Application Kokai No. 4-39,665) and the like. However, it has ben pointed out that these chemically amplified resists have the respective inherent problems and various difficulties accompany the putting them to practical use. That is to say, in the system in which a resin having a tert-butyl ester group or a tert-butoxycarbonyl group is used, the chemical reaction based on the catalytic action of the acid generated is accompanied by the liberation of a gas component such as an isobutene gas or a carbon dioxide gas, so that the volume shrinkage is caused upon irradiation with a radiation, and consequently, the pattern shape tends to be distorted and hence the formation of a high precision pattern is difficult. The system in which a resin having a silyl group is used has a good pattern-formability; however, it has such a disadvantage that as compared with other systems using a resin free from silyl group, it is inferior in peelability from a substrate. In addition, in the system in which a resin comprising an acrylic acid component is used, there is such a disadvantage that the adhesiveness between the resist and the silicon substrate is insufficient, and there is such a problem that the dry etching resistance is lower than that of a resist using an aromatic resin.
In order to solve the above-mentioned problems, attention has recently been paid to resins having both acrylic acid ester structure and phenol skeleton (see, for example, Japanese Patent Application Kokai Nos. 4-251,259; 5-181,279 and 5-113,667).
Resists using these resins have such advantages that the dry etching resistance is improved as compared with that of a resin having only an acrylic acid recurring unit. However, since a carboxylic acid is formed in the exposed portion, the solubility-in-alkali-developer rate becomes too high, and there is such a disadvantage that when a resist pattern is actually formed on a substrate, the upper part of the pattern formed becomes too thin to form an ideally rectangular pattern.